1. Field of the Invention
The present invention provides a process for preparing aryl diesters from aromatic hydrocarbons such as benzene, naphthalene, anthracene, phenanthrene, fluorene, biphenyl, terphenyls, and the like, which comprises reacting a mixture of the aromatic hydrocarbon, for instance naphthalene, a carboxylic acid, and molecular oxygen in the liquid phase in the presence of a catalyst consisting essentially of palladium or a compound of palladium, a compound of antimony and a compound of at least one member selected from the group consisting of an alkali metal, chromium, zinc, antimony and tin.
2. Description of the Prior Art
The manufacture of phenol by direct oxidation of benzene with oxygen is known. There are, for instance, thermal processes which are performed at very high temperatures in which phenol formed is susceptible to further oxidation so that considerable loss of yield occurs as is disclosed in U.S. Pat. No. 2,223,383. In the presence of catalysts, the oxidation can be carried out at somewhat lower temperatures as in U.S. Pat. No. 3,133,122, but the reactions have been plagued by low conversions and excessive production of unwanted by-products as discussed in U.S. Pat. No. 2,392,875.
It has already been proposed to make phenyl acetate and biphenyl from benzene and acetic acid in the liquid phase in the presence of palladium acetate and without added molecular oxygen by a stoichiometric reaction in Chem. and Ind., Mar. 12, 1966, Page 457.
U.S. Pat. No. 3,542,852 discloses the preparation of hydroxy aromatic compounds by reaction of an aromatic compound and oxygen in the presence of a catalyst composed of iron, a noble metal or a compound of either in the presence of a nitrate ion and a carboxylic acid. More recently, the preparation of phenyl esters and phenols by the reaction of benzene, molecular oxygen and a lower aliphatic carboxylic acid in the presence of a catalyst composed of a Group VIII metal (U.S. Pat. No. 3,642,873) or a compound of such metal (U.S. Pat. No. 3,651,127) have been disclosed. Similarly, variations in this type of reaction have been disclosed in U.S. Pat. Nos. 3,646,111; 3,651,101; 3,772,383; 3,959,352 and 3,959,354. U.S. Pat. No. 3,959,354 concludes that liquid phase reactions of this type because of problems of catalyst elution, etc., are disadvantageous for an industrial process. U.S. Pat. No. 3,772,383 describes a liquid phase reaction using a very complex catalyst system which includes the use of nitric acid and a lower aliphatic carboxylic acid. U.S. Pat. No. 3,644,486 discusses the production of acylation products of condensed aromatic compounds in the liquid phase with oxygen and a saturated carboxylic acid in the presence of a noble metal or compound thereof.
Generally speaking, these prior art processes deal for the most part with vapor phase oxidation reactions, or liquid phase reactions in which all the reactants (except oxygen in some instances) are initially included in the reaction mixtures. Moreover, in general the prior art catalytic processes have produced very low conversions, usually less than 10%, with low selectivity to the desired monophenyl ester, and phenol or phenolic materials are often a primary product of the oxidation reaction. None of the prior art processes show the production of diacyloxy products nor do any of them show the continuous removal of water from the reaction mixture as it forms.